In electric installations, the above-mentioned industrial switching devices and others are normally operated or monitored centrally by means of a control system, for instance, by means of a programmable logic controller (PLC). Typically, the switching devices are connected to the control unit (e.g. the PLC) via the control wiring lines. As a rule, this control unit comprises the lines that can turn the switching device, here preferably a contactor, on and off, and that, at the same time, provide the requisite power for operating the switching device and it comprises lines that return the signals from the switching device to the control unit for monitoring purposes. Examples of signals for monitoring a switching device, here especially a motor starter, are the status of the contactor switching position (ON/OFF) or the status of the motor circuit breaker (ON/tripped).
When an electric installation (for instance, a switch cabinet) is being set up, the wiring and interconnection of the electric switching devices with the control system are usually done manually, typically by electricians. This work can often be a very time-consuming part of the set-up of the switch cabinet. Moreover, the wiring via many similar control lines is error-prone since, for example, they can be inadvertently mixed up when they are laid in the cable conduits, as a result of which they might be connected to terminals of the wrong devices. Furthermore, the control lines have to be laid to the individual switching devices in order to be electrically connected there. This calls for additional work to the effect that cable conduits for laying the lines have to be specifically cut to length and mounted on the assembly plate, and the individual control lines can then be laid in these cable conduits.
The devices may be interconnected between a bus and other components of a system. European patent application EP 0 779 640 A2 describes, for instance, the use of bus-compatible amplifier modules for drive assemblies of electric switching devices. The electromagnetic or electronic amplifier assembly is connected via an interface circuit to bus connectors and, on the one hand, to feed current connectors and, on the other hand, to drive connectors. The interface circuit is configured to be bidirectional or unidirectional. Moreover, switching means are provided for signals that are to be taken over from the bus for setting parameters of the amplifier module and/or of the switching device as well as switching means for picking up signals that are to be transmitted to the bus about the states of the amplifier module and/or of the switching device.
Regarding coupling to a bus, European patent application EP 0 637 784 A1 describes a module that is provided with a bus coupler which, on the one hand, is connected to a contact system for the electric and mechanical connection to the bus and, on the other hand, to an electronic evaluation unit for the programmed processing of measured signals or state information as well as for issuing switch-off commands, whereby the measured signals or state information are fed via the bus. The module itself can construct switch-off commands by processing the measured signals and then relaying them to the tripping system for a circuit breaker.
German patent application DE 101 47 442 A1 describes a method and a device as well as a control unit for monitoring a bus system having at least three subscribers, whereby one subscriber is configured as the superordinated subscriber and it initiates every data transmission to the bus system. A second subscriber is configured as an element of a locking system of a lockable interior of a vehicle, while a third subscriber is configured so as to be outside of the lockable interior of a vehicle. The first subscriber monitors the data transmission in such a way that, in at least one operating state of the vehicle and/or the bus system, the first subscriber initiates measures to prevent the transmission of data in the case of every data transmission to the bus system that was not initiated by said subscriber itself. A LIN bus system is employed as the bus system.
German patent application DE 101 47 446 A1 also describes a method and a device for monitoring a bus system having at least two subscribers, of which at least one is configured as an authorized subscriber, and it monitors the data transmission to the bus system, whereby, an identifier is transmitted with every data transmission to the bus system, and this identifier can be unambiguously associated with a subscriber. If the data transmission is initiated by an entity other than an authorized subscriber, the execution of the data to be transmitted is prevented. A LIN bus system is employed here as well.
German patent application DE 197 56 918 A1 describes a communication control device in which a master station transmits a batch transmission frame to a plurality of slave stations, and individual response frames are transmitted from the slave stations to the master station.
DE 689 20 028 T2 describes a method and a device that allows multiple access with cyclical reservation in a communication system, whereby access is provided to the transmission medium in the communication network with a unidirectional bus structure in a folded-bus configuration or in a double-bus configuration and a plurality of stations that are connected between the buses. The network comprises two unidirectional, opposite transmission buses and a plurality of stations, each of which is connected to the two buses. There is also a head end that generates times slots at regular intervals on the buses, whereby each station requests access to a slot.
German patent application DE 34 24 866 A1 describes a method and an arrangement for the transmission of data, whereby the latter is transmitted in a time-division multiplex in digital form in a bus system. The bus system consists of a central control unit, several equivalent subscribing stations subordinated to the control unit, and at least one data bus line that connects all of the subscribers.